Method of controlling continuously variable transmission

Abstract

The method features in that the speed at which a shift actuator operates in effecting an upshifting is slower than the speed at which the shift actuator operates in effecting a downshifting.

We claim: 
     
       1. A method of controlling change in reduction ratio in a continuously variable transmission of a motor vehicle, wherein the rate of change in reduction ratio in the continuously variable transmission with respect to time is adjustable by a shift actuator in response to a speed at which the shift actuator operates, the method comprising the steps of: detecting operating conditions of the motor vehicle;   determining a desired optimum reduction ratio indicative signal indicative of a target operating position of the shift actuator which corresponds to a desired optimum reduction ratio for the detected operating conditions of the motor vehicle;   generating an actual reduction ratio indicative signal indicative of an actual operating position of the shift actuator;   comparing said actual signal with said desired signal and generating a first signal when an upshift is required and a second signal when a downshift is required;   causing the shift actuator to operate at a first predetermined speed in a first direction in response to the presence of said first signal; and   causing the shift actuator to operate at a second predetermined speed in a second direction which is opposite to the first direction in response to the presence of said second signal;   said first predetermined speed being slower than said second predetermined speed.   
     
     
       2. A method of controlling a continuously variable transmission comprising a shift actuator which is rotatable in a first direction in effecting a shifting toward a small reduction ratio and in a second direction which is opposite to the first direction in effecting a shifting toward a large reduction ratio, the method comprising the steps of: determining whether a reduction ratio should change toward a small reduction ratio or toward a large reduction ratio;   operating the shift actuator in the first direction at a first predetermined speed in effecting a shifting toward the small reduction ratio when the reduction ratio should change toward the small reduction ratio;   operating the shift actuator in the second direction at a second predetermined speed in effecting a shifting toward the large reduction ratio when the reduction ratio should change toward the large reduction ratio,   said first predetermined speed being slower than the second predetermined speed.   
     
     
       3. A method as claimed in claim 2, wherein said determining step includes a step of comparing a signal indicative of an actual operating position assumed by the shift actuator with a signal indicative of a desired operating position to be assumed by the shift actuator. 
     
     
       4. A method as claimed in claim 2, wherein said determining step includes a step of comparing a signal indicative of an actual engine revolution speed with a signal indicative of a desired engine revolution speed. 
     
     
       5. A method as claimed in claim 2, wherein said determining step includes a step of comparing a signal indicative of an actual reduction ratio with a signal indicative of a desired reduction ratio. 
     
     
       6. A method of controlling change in reduction ratio in a continuously variable transmission of a motor vehicle, the continuously variable transmission having a V-belt running over a drive pulley and a driven pulley, a shift actuator having a plurality of operating positions, a source of hydraulic fluid pressure, means actuated by the shift actuator for regulating fluid supply to and fluid discharge from at least one of the drive pulley and driven pulley so as to establish a reduction ratio that is predetermined for one of the plurality of operating positions of the shift actuator, said method comprising the steps of: detecting operating conditions of the motor vehicle;   generating a desired operating position of the shift actuator for the operating condition of the motor vehicle detected;   generating a parameter that is set to a predetermined value whenever the continuously variable transmission attains only a single predetermined condition;   comparing said parameter with said desired operating position and generating a first signal when said parameter is to be varied in a first direction and a second signal when said parameter is to be varied in a second direction that is opposite to said first direction;   varying said parameter at a first predetermined speed in said first direction in response to the presence of said first signal, but at a second predetermined speed in said second direction which is opposite to said first predetermined direction; and   causing the shift actuator to operate in an open loop manner in response to a variation in said parameter.   
     
     
       7. A method of controlling change in reduction ratio in a continuously variable transmission of a motor vehicle, the continuously variable transmission having a V-belt running over a drive pulley and a driven pulley, a stepper motor having a plurality of rotary positions, a source of hydraulic fluid pressure, means actuated by said stepper motor for regulating fluid supply to and fluid discharge from at least one of the drive and driven pulleys so as to establish a reduction ratio that is predetermined from one of the plurality of rotary positions of the stepper motor, said method comprising the steps of: detecting operating conditions of the motor vehicle;   generating a desired pulse number indicative of a desired rotary position of said stepper motor for the operating condition of the motor vehicle detected;   generating an actual pulse number that is set to a predetermined value whenever the continuously variable transmission attains a predetermined condition;   comparing said actual pulse number with said desired pulse number and generating a first signal when said actual pulse number is less than said desired pulse number and a second signal when said actual pulse number is greater than said desired pulse number;   varying said actual pulse number at a first predetermined speed in a first direction in response to the presence of said first signal, but at a second predetermined speed in a second direction which is opposite to said first direction in response to the presence of said second signal; and   causing the stepper motor to rotate in an open loop manner in response to a variation in said actual pulse number.